In an effort to reduce emissions and to comply with more strict clean air standards, manufacturers of various diesel engine components have begun exploring alternative engine strategies. One such strategy that appears to have promise is the alteration of the manner in which fuel is injected. For instance, in a traditional diesel engine, fuel injection is timed to occur when the cylinder piston is near a top dead center position for its compression stroke. When the fuel and air reach an auto-ignition point, combustion occurs. This can be virtually instantaneous or after some ignition delay.
Engineers have learned that it is possible to reduce engine emissions if a small amount of fuel is injected while the cylinder piston is at the beginning of the compression stroke. In other words, when the piston is closer to a bottom dead center position than the top dead center position for the compression stroke. The injected fuel mixes with the air as it is being compressed to form a relatively homogeneous mixture that combusts when the piston is near its top dead center position. This mode of operation is typically referred to as homogeneous charge compression ignition. Because the fuel mixture is relatively homogeneous when combustion occurs, fewer emissions are produced during this type of injection event than a typical injection event. In other words, uniform air/fuel distribution and associated lower combustion temperatures contribute to significant NOx, and particulate reductions.
One example of an engine utilizing the homogeneous charge compression ignition is described in U.S. Pat. No. 5,875,743, which issued to Dickey on Mar. 2, 1999 and is entitled Apparatus and Method For Reducing Emissions in a Dual Combustion Mode Diesel Engine. The apparatus disclosed by Dickey includes a port diesel fuel injector that is capable of delivering fuel to an engine cylinder for a homogeneous charge compression ignition injection event in addition to a fuel injector positioned to perform a more traditional injection event. While the fuel injection system of Dickey is capable of reducing emissions, there is still room for improvement.
For instance, engineers have determined that a reduction in the number of engine components can result in a more robust operating system. As indicated, the fuel injection system taught by Dickey includes multiple fuel injectors for the performance of two distinct injection events. However, it should be appreciated that the fuel injection system could be more robust if there was only a single fuel injector which had a limited number of components. In other words, a reduction in the number of fuel injectors, and/or fuel injector components, could make the system more robust because there would be less components that could fail or malfunction. In addition, in contradiction to the teachings of Dickey, engineers have learned that for certain engine load conditions, homogeneous charge compression ignition events may not be desirable.
The present invention is directed to overcoming one or more of the problems set forth above.